1. Field of the Invention
This invention relates in general to an electrolytic cell for generating halogen biocides and oxygen for liquid treatment, and more particularly to an improved electrolytic cell configuration for reduction of electrode plate deterioration.
2. Description of the Prior Art
Chlorine has been used extensively for a long time as a biocidally active agent for treating both non-potable liquids such as sewage, effluents, swimming pool water, spa water, cooling tower water, and potable water from wells, reservoirs and the like.
Chlorination has traditionally been accomplished by the addition of chemical compounds, such as a hypochlorite compound, to the liquid being treated. The addition of chemical compounds for producing the desired biocidal activity has become increasing costly due to the costs for purchasing the compounds. In relatively large installations, such as cooling towers, water condition sensing devices are used in conjunction with dispensing equipment for more or less automatic operation. Such devices and equipment are also very costly not only from a purchasing standpoint, but also from operating and maintaining standpoints. In relatively smaller installations such as many swimming pools and spas where atuomatic sensing and dispensing equipment cannot be economically justified, manual testing and compound dispensing must be done on a regular basis. However, due to busy schedules, forgetfullness and the like, manually accomplished water treatment is often neglected.
In addition, the storage and handling of such chemical compounds is dangerous, and it is very likely that increasingly stringent regulations will be imposed on the transporting of dangerous chemicals, and this will add to the costs of such products which are already expensive.
A solution to many of these problems is to employ and electrolytic cell for on-site production of a biocidally active agent at a reasonable cost, greater ecological acceptability and improved safety. An electrolytic cell produces a halogen biocide from an aqueous solution which contains a halogen salt, such as producing chlorine by electrolysis of water containing sodium chloride, such as sea water. However, all too often, cooling towers, swimming pools, wells and the like, are located in areas where only fresh water is available. In those areas, electrolytic generation of low levels of chlorine has been hampered by low current efficiencies in fresh water containing low levels of the chloride salt, and by excessive formation of scale on the cathode ot the electrolytic cell. One method for overcoming this is to utilize an aqueous solution having a high concentration of chloride salt for producing chlorine by electrolysis. The chlorine generated in this manner is mixed with a suitable carrier liquid, and then in turn, added to the liquid being treated. While the current efficiencies in the cells used in accordance with this method are good, the mechanism used for safely mixing the chlorine, or other biocidally active agent with the carrier liquid are complex and have become increasingly expensive. Due to the complexity of the equipment, extra handling of the biocidally active agent and the like, the use of this method has exhibited poor field performance.
For the above reasons, I devised an electrolytic cell for direct generation of a halogen biocide from solutions containing very low concentrations of halogen salts. My cell, which is fully disclosed in U.S. Pat. Nos. 4,100,152 and 4,202,738, is manufactured at commercially feasible prices for low-cost onside generation of halogen biocides directly from the aqueous solutions which are passed through the cell. This special electrolytic cell includes a plurality of planar electrode plates which are provided with special surface coatings and are arranged in spaced apart parallel relationship with respect to each other within an enclosure through which the solution to be treated is passed. Electric connection is made from a suitable power source to a centrally located one of the electrode plates and to each of the outermost and oppositely located electrode plates. These electrode plates which are connected to the power source are referred to as the primary electrode plates, and the other plates which are located between the primary electrode plates are not connected to the power source and are commonly referred to in the art as bipolar electrode plates.
Although the above mentioned U.S. Patents describe the electrolytic cell operation as having ionic current flow therethrough in a fixed direction with cell operation being intermittent for electrode plate cleaning purposes, it was found that periodically reversing the polarity of the primary electrode piates worked better for plate cleaning purposes. Even so, the electrolytic cell must be removed from the solution moving system from time to time to remove scale deposits which build up rather rapidly particularly at the exposed end edges of the primary electrode plates. Although the need for removal of the cell from the solution moving system is less than ideal, the major problem is electrode deterioration which takes place in the same areas where excessive scaling occurs.
Due to the hostile environment in which the electrolytic cell operates and the rather stringent plate mounting requirements, the cells must be manufactured in a way which makes it virtually impossible, at least at an on-site location, to replace one or more deteriorated electrode plates. Therefore, even though these electrolytic cells have significant benefits from cost, convenience, safety and other standpoints, in comparison to the other herebefore described devices and methods, the electrolytic cell must be removed and cleaned more frequently than is desirable, and the entire cell must be replaced at intervals which are less than ideal.
Therefore, a need exists for a new and improved electrolytic cell which overcomes, or at least substantially reduces the scaling and electrode plate deterioration problems of the prior art.